A Novel Concept of TE₂₀-Mode 90° Waveguide Twist With Mode Filtering Characteristics

We present a novel TE20-mode 90° waveguide twist concept for millimeter-wave (mm-wave) and terahertz (THz) applications. This waveguide twist has the unique characteristic of mode filtering; that is, only the desired TE20 mode can be rotated and output, the fundamental TE10 mode, and higher order modes will be reflected. In the design, the input/output (I/O) channels are orthogonal oversized waveguides, the TE20 mode is converted into a cross-waveguide (cross-WG) with gradually changed arm lengths. Broad bandwidth (BW) and high efficiency can be easily achieved in a compact size. To verify the proposed concept, two 160–270-GHz prototypes based on rectangular waveguides (RWGs) and groove gap waveguides (GGWs) were designed, fabricated, and measured. The RWG-based prototype was milled in one metal block, while the GGW-based one was fabricated in two metal split blocks. The measured results reveal that the two prototypes achieve average insertion losses of 0.21 and 0.36 dB for the interested TE20 mode, and minimum suppressions of 45 and 35 dB for the unwanted TE10 mode over the desired frequency band. The features of polarization rotation and mode filtering make the proposed TE20-mode waveguide twist be a candidate for compact, broadband, and efficient waveguide systems.